fix(uart): Permit UART speeds over 460800 on ESP32 Arduino 3.0

[ewpa]

Description of Change

Regression fix: Permit UART speeds over 460800 on ESP32 Arduino 3.0 and later. UART speeds above 460800 were functional on ESP32 Arduino 2.0.

Tests scenarios

Tested on ESP32 Arduino 3.0.5.

Related links

• b1ackviking: "Console sets UART clock source to REF_TICK on ESP32 and ESP32S2 by default, however, APB clock frequency does not change when power management is disabled. Using APB clock source allows higher baud rates for UART console."
• Merge espressif/esp-idf PR#8572: "fix(console): use apb clock source for uart when power management is disabled (IDFGH-6952)"
• Closes Issue UART speeds above 460800 on ESP32 no longer functional since v3.0. #11024.

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👋 Hello ewpa, we appreciate your contribution to this project!

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[SuGlider]

@ewpa -
ESP32 Arduino has all SoC with CONFIG_PM_ENABLE disabled:
sdkconfig

#
# Power Management
#
# CONFIG_PM_ENABLE is not set
# CONFIG_PM_SLP_IRAM_OPT is not set
# end of Power Management

The suggested change (testing #elif defined(CONFIG_PM_ENABLE) && SOC_UART_SUPPORT_REF_TICK) would simply remove part of the code forever:

  // there is an issue when returning from light sleep with the C6 and H2: the uart baud rate is not restored
  // therefore, uart clock source will set to XTAL for all SoC that support it. This fix solves the C6|H2 issue.
#if SOC_UART_SUPPORT_XTAL_CLK
  uart_config.source_clk = UART_SCLK_XTAL;  // valid for C2, S3, C3, C6, H2 and P4
#elif defined(CONFIG_PM_ENABLE) && SOC_UART_SUPPORT_REF_TICK
  if (baudrate <= REF_TICK_BAUDRATE_LIMIT) {
    uart_config.source_clk = UART_SCLK_REF_TICK;  // valid for ESP32, S2 - MAX supported baud rate is 250 Kbps
  } else {
    uart_config.source_clk = UART_SCLK_APB;  // if power management is enabled baudrate may change with the APB Frequency!
  }
#else
  // Default CLK Source: CLK_APB for ESP32|S2|S3|C3 -- CLK_PLL_F40M for C2 -- CLK_PLL_F48M for H2 -- CLK_PLL_F80M for C6
  uart_config.source_clk = UART_SCLK_DEFAULT;  // baudrate may change with the APB Frequency!
#endif

If the baudrate is set to 460,800, it will be over REF_TICK_BAUDRATE_LIMIT (250,000) and the UART Source Clock will be set as UART_SCLK_APB, which is the same as UART_SCLK_DEFAULT.

Please explain how this PR would be effective for the issue you have presented.

[ewpa]

Hi @SuGlider, thank you for taking a look. What you are saying makes sense so I will need to review this PR further to see why it appears to make a positive impact in my case (i.e. UART rate of 921600 and above).

[SuGlider]

This change is not recommended.

[ewpa]

Agreed, I withdraw this PR. See Issue #11024 for alternatives.